The invention set forth in the specification pertains to synthetic polymer irrigation tubing with improved discharge holes or openings.
Currently large amounts of synthetic polymer irrigation tubing are used for a wide variety of agricultural and related applications. Such tubes are normally formed by the extrusion of a synthetic polymer or polymer composition which is comparatively flexible when present in a comparatively thin sheet or the like and which is substantially rigid when used in significantly thicker sheet or body into a cylindrical tube and then by forming a series of discharge holes in the wall of such a tube. Of course there are many variants on this procedure. For example, a well known type of irrigation tubing is formed by extrusion so that a "dome" appearing much as half of a cylinder is located on a cylindrical tube and holes are drilled connecting the interior of the cylinder with the partial cylinder and connecting the interior of the latter with the outside of the complete tube. This type of tubing is commonly referred to as "Bi-Wall" tubing.
Structures such as the latter have been developed because of the fact that for some applications it has been impossible to drill holes in tubing which are of such a character that under normal conditions of use only extremely limited quantities of water will flow through them. It is believed that such holes have always been cylindrical or nearly cylindrical in shape and configuration. In accordance with concepts dating back to Roman civilization such holes have on occasion been slanted relative to the interiors of such tubes to control flow. Many of the variants on traditional cylindrical tubing are intended to overcome this problem of the holes in irrigation tubes passing more than desired amounts of water.
Thus, for example, the "Bi-Wall" tubing indicated in the preceding is intended to and does in fact limit the amount of water dispensed as it is used by achieving a pressure step down effect. In other words water in the cylindrical tube in such a structure will flow though the holes to the partially cylindrical "add on" tube at a rate which is determined in part by the differential in the pressure between the two tubes, in part by the dimensions of the holes connecting them and by other factors and, in turn water will be distributed to the ambient by the pressure gradient between the secondary add-on tube and the ambient and the dimensions of the holes leading to the exterior of the tubing.
An understanding of the present invention does not require a detailed understanding of all of the different structures and expedients which have been proposed and, to varying extents, used and accepted as suitable of use in dispensing only very limited quantities of water from the interior of an irrigation tube. It is considered obvious that any irrigation tubing in which other than holes formed in the wall of the tube are used to dispense water will be more expensive than tubing in which peripheral holes in the wall of a tube are used for this purpose. This is significant with the invention since in the field of the invention minor differences in costs can be critical from a commercial standpoint.